Gas metal arc welding torches, including metal inert gas (“MIG”) torches, are widely used to weld metallic materials. A welding torch is designed to allow a user or robot to direct a metal welding wire toward a specific location on a target metal workpiece. As illustrated in FIG. 1, the components of a known welding torch include a handle 12, a gooseneck 14 (sometimes called a mounting tube or a conducting tube), a retaining head 16, a contact tip 18, and a nozzle 20. In some MIG torches, a diffuser is employed rather than a retaining head. The welding torch can be connected to a robotic arm via a mount, 22, or it can be hand held and trigger operated. A welding wire is fed through the handle of the welding torch and ultimately through a passageway in the contact tip, which is disposed at a proximal end of the welding torch. The welding wire is consumed as the welding process progresses and is replenished from a distal wire spool. The welding wire and workpiece material are melted and combined in a molten welding pool.
Referring now to FIG. 2, in a conventional MIG welding torch, a liner 24 passes through a channel 28 within the gooseneck 14 towards the retaining head 16. The liner 24 is secured, if at all, by the longitudinal pressure of the liner 24 against the retaining head 16. Since the liner 24 is relatively long compared to the other components, the precise liner 24 length required to achieve a desired longitudinal positioning pressure against the retaining head occurs only by happenstance and is thus very unlikely.
Referring to FIG. 3, a shield gas used during torch operation typically flows toward the retaining head through an annular space 30 that is located between the gooseneck 14 and the liner 24. The shield gas passes out of the retaining head 16 through at least one vent hole 34 and exits the torch through the nozzle 20. The precise proximal longitudinal termination point of liner 24 generally is uncertain and not repeatable. This uncertainty results in radial and longitudinal motion of the liner 24 during torch operation, causing abrasion and premature wear of the liner 24, the retaining head 16, and other adjacent parts. Additional axial motion of the liner 24 is also caused by thermal expansion and contraction of the torch components as the torch head heats and cools with cyclical usage.
One known method to overcome these problems is illustrated in FIG. 4. A set screw 45 can be used to secure the liner 24 to an inside wall of the retaining head 16 or gooseneck 14. Although this tends to reduce the movement of the liner 24, the liner 24 is not axially centered within the gooseneck 14 or the retaining head 16. As the set screw 45 is tightened, establishing and maintaining a longitudinal termination point of the liner 24 becomes difficult. Even after the liner 24 is secured, this method does not adequately prevent longitudinal movement of the liner 24 as the torch is moved and does not properly maintain alignment of the liner 24. Accordingly, excessive abrasion occurs as the weld wire passes through the proximal end of the liner 24, the gooseneck 14, and/or the retaining head 16, which tends to damage components of the welding torch, including the contact tip 18.
The components of a welding torch typically have screw threads for attachment to the welding torch or other components. Unfortunately, these threaded connections tend to loosen as the welding torch is used, requiring users to stop welding to re-tighten these connections, resulting in down time and losses in efficiency and productivity. In addition, loose connections can be a source of electrical resistance that generates excessive heat within a welding torch. Heat in welding torches translates into shorter consumable life, contact tip burn back, and even melting of components.